The present disclosure relates to an image forming apparatus such as a copier, a printer, a facsimile machine, etc., and to a developing device and a developer carrying member that are incorporated in such an image forming apparatus. More particularly, the present disclosure relates to a method for suppressing deformation of a fixed magnet member arranged in a developer carrying member.
In one conventionally common process as an image developing system in image forming apparatuses exploiting an electrophotographic process, powder developer is mainly used, an electrostatic latent image formed on an image carrying member such as a photosensitive drum is made visible with the developer, and the visible image (toner image) is transferred to a recording medium and is then fixed.
Developer is roughly classified into two-component developer containing toner and magnetic carrier and one-component developer containing non-magnetic or magnetic toner alone. In one known developing system using two-component developer, a magnet (magnetic pole) having a magnetic field that varies in strength in the circumferential direction is fixed to a central part of a developing roller (developer carrying member), and a metal regulating blade is arranged opposite the surface of the developing roller across a gap of several hundred micrometers.
On the other hand, as a developing system using one-component developer, a so-called jumping one-component developing system is known in which a fixed magnet member having a plurality of magnetic poles is arranged inside a developing roller, toner in a developer container is carried on the developing roller by use of a magnetic carrying force, a thin layer of toner is formed through layer thickness regulation by use of a regulating blade, and toner is made to fly to the photosensitive drum at a developing position.
In recent years, as a magnet that is arranged inside a developing roller, a plastic magnet formed of a resin material having magnetic powder dispersed in it is used. Plastic magnets can hold higher magnetic forces in small volumes as compared with rubber magnets. Plastic magnets, however, are more expensive than rubber magnets.
As a compromise, configurations are known in which, for example, as a magnetic pole which requires a strong magnetic force such as a main magnetic pole, a plastic magnet is arranged, and as a sub-magnetic pole, an inexpensive rubber magnet is arranged.